The present invention relates to clutch mechanisms for engaging a rod for longitudinal movement. The invention is particularly, though not exclusively, applicable to actuators for hand-held devices, such as applicators for dispensing viscous material.
Applicators for fluids, such as sealants, mastic and other compounds of a thick or pasty nature, are well known. Their basic design has not changed over many decades. Typically, they comprise a frame supporting a yoke in which a cartridge of the compound is positioned. The compound is dispensed from a nozzle as a plunger on a rod advances into the cartridge. An actuating mechanism is also mounted on the frame. This comprises an apertured drive plate mounted on the rod which is engaged by a trigger. As the trigger is squeezed, it tilts the plate to engage the rod and, thereafter, move the rod forwardly. In this sense the inventors have come to view the plate as a form of clutch, harnessing the trigger movement and imparting it to the rod. An apertured brake plate is mounted on the rod behind the drive plate. This is biased into engagement with the rod to allow the rod to advance but prevent it from retreating until it is released manually.
The prior art mechanisms are around 50% efficient based on the ratio of effort applied to the trigger in relation to the resultant force at the plunger. A major contributory factor to this level of inefficiency is the binding of the rod in the bores in the frame by which the rod is supported. The friction problem is caused by the bending moment imposed on the rod by the trigger acting on the drive plate. As the force on the drive plate is applied to one side of the rod, the force transmitted to the rod is out of balance. In heavy duty applications this bending moment is a significant contributory factor to the overall diminution of efficiency.
It has been proposed in EP-A-0645194 to address this by balancing the forces applied by using two drive plates one on either side of the rod, that are engaged by the trigger coincidentally. This has some beneficial effect, but the catch plates are arranged one behind the other, producing some bending moments between them. The proposed system still requires off-centre plates extending in opposite directions. Also, there are still only two points of contact for each plate on the rod.
It is an object of the present invention to provide a balanced clutch mechanism for a rod.
According to the present invention there is provided an clutch mechanism for a rod comprising a body having first and second ends and an aperture partially defined by a wall having a converging portion, through which aperture the rod extends between first and second ends of the body, rod engaging means within the body moveable relative thereto between an engaged position towards the first end of the body, in which the bearing means are engaged between the wall and the rod such that the rod is fixed relative to the body when a force is applied to the first end of the body, and a disengaged position towards the second end of the body, in which the rod is movable relative to the body.
The present invention provides an clutch mechanism that embraces the rod in which the means for engaging the rod are retained within the body. The force on the rod is applied through the body which can be engaged as necessary.
Preferably, the rod engaging means are spaced around the rod to distribute the load evenly.
The engaging means may be adapted for rolling contact e.g. balls, preferably ball bearings, or rollers, or slidable members such as wedges.
Preferably, the converging wall defines the guide surfaces so that the engaging means are entrained to movement axial to the rod. The engaging means may additionally have a spacer means, for example a cage, for maintaining them in their respective positions.
To allow the mechanism to operate in any orientation the engaging means are preferably biased to the engaged position. The mechanism may then also be provided with a release mechanism by which the engaging means are urged from the engaged position.
The invention also extends to a hand tool incorporating a clutch mechanism as defined. More particularly, the invention extends to a dispensing mechanism incorporating a clutch mechanism as defined. The use of the mechanism in a hand tool is particularly advantageous as it addresses the particular problem of the off-axis driving force and is, therefore, of particular benefit.
The clutch mechanism can also be used as a braking clutch as well as a means of engaging a rod to drive it.